1. Field of the Invention
This invention is directed to vibratory separators; to apparatuses and methods for sensing fluid levels in such separators; and to apparatuses and methods for adjusting such levels and for adjusting the extent of a beach area on a screen.
2. Description of Related Art
In many prior art vibratory separators and shale shakers a pool or mass of fluid or material is formed on top of one or more screens or screen assemblies which are used to filter material introduced to the separator or shaker. The depth of this fluid or material can affect efficient operation of the separator or shaker. Fluid or material that is too deep may not be adequately filtered. Fluid or material that is too shallow may flow across a screen too quickly or without sufficient weight to be filtered adequately.
Shale shakers assist in maintaining certain desired properties of drilling fluid by using vibrating screens to remove certain large particles while allowing certain smaller particles to remain in the fluid. The large undesirable particles may include drilling cuttings and debris picked up in the drilling process. The smaller particles may include drilling fluid additives that are required for maintaining desired drilling fluid density and viscosity. The screens on these shakers have a limited life, and can be expensive and time consuming to replace. The shaker is turned off and, preferably, rinsed clean prior to screen replacement.
One factor in screen life is how well the beach area is maintained. “Beach” area is the distance from a fluid-dry interface-with-fluid line on a final screen to the end of the screen. Thus, a zero beach length describes a shaker operating with drilling fluid covering the entire screen area of the final screen and running over to discharge. This can be costly due to the loss of drilling fluid which flows off, rather than through, a screen. A beach length of 20″ in certain shakers indicates a shaker operating fairly dry, with the last sections of screen potentially vibrating against completely dry particles. Such dry particles vibrating on the beach of the last screen can tear holes in the screen and shorten the screen life. The beach length is affected by variables such as fluid flow rates and drilling fluid properties including viscosity, density, temperature, and solids content.
In many prior art separators and shakers tilting or raising mechanisms are provided to adjust the angle of screen(s) with respect to the horizontal. For example, a prior art shaker S (shown in FIG. 1) has a tilting mechanism which permits a screen-containing basket to be tilted around a pivot point P up to 5° from the horizontal.
U.S. Pat. No. 4,082,657 discloses a separator apparatus which has individual height adjustable mounting structures for each screen unit which permit adjustment of the screen unit angle with respect to the horizontal.
U.S. Pat. No. 6,575,304 B2 discloses an hydraulic ram apparatus beneath a screen body which is used to adjust the angle of incline of the screen body.
In many prior art systems, a determination of the level of material or fluid on a screen or screen assembly of a separator or shaker is done visually and then adjustments of screen incline angle or of screen support incline angle are done manually.
There has long been a need, recognized by the present inventors, to provide an efficient and accurate measurement of the depth of fluid or material on a screen or screen assembly of a vibratory separator or shale shaker. There has long been a need, recognized by the present inventors, for such separators and shakers with accurate adjustment of such depth based on measurement thereof. There has long been a need, recognized by the present inventors, for a shale shaker or vibratory separator with screen pool depth adjustability to efficiently adjust last-screen beach extent to enhance screen efficiency and to prolong screen life.